Plunger switch



N. M KINNEY PLUNGER SWITCH Jan. 3, 1939.

Filed Dec. 14, 1937 w c R M m R NU E E0 T w@ r 0 NH VI Patented Jan. 3,1939 UNITED STATES PATENT OFFICE PLUNGER SWITCH Application December 14,1937, Serial No. 179,839

2 Claims.

My invention relates to an electric circuitbreaker, and particularlyrelates to liquid contacts for completing an electric circuit.

Heretofore, mercury tube switches have been employed to open or closeelectrical circuits. Although it has been found that the mercury willtake part of the arc when the circuit is broken, nevertheless theelectrode from which the mercury recedes when the circuit is brokentakes part of the arc and eventually becomes pitted and deteriorated.Various structures have been proposed from time to time in which thecontact wear and erosion are greatly reduced.

Provisions have been made to surround one of the fixed electrodes in theswitch with mercury, but the problem has always arisen as to the mannerof sealing a cup or other suitable container for the mercury about oneof the electrodes and which cup will withstand the change intemperatures to which the unit is subjected. As different elementsexpand and contract at diflerent rates, one element may have acoefiicient of expansion different from the other element so that abreaking of the fragile insulator element occurs. This difiiculty hasresulted in practically no successful commercial mercury switches beingused wherein electrical contacts of mercury as one conductor engagesanother portion of mercury as the second conductor. r

With the above difilculties to be overcome, it is an object of myinvention to utilize a liquid conductor for making and breaking anelectric circuit within a sealed container.

Another object of my invention is to construct a mercury electric switchof material so that electrolysis will not form a permanent electricalcircuit.

Another object of my invention is to provide a circuit making andbreaking unit in which a new electrical contact surface is provided ateach make and break of the circuit and in which the contacts aremaintained in a clean condition by reason of the quick movement of theplunger which displaces a portion of the contact forming liquid so thatan electrical contact is formed.

Another object of my invention is to provide two electrodes within asingle housing which electrodes emerge from the same area or base-thisstructure enables both electrodes to be simultaneously sealed andeliminates one operation over the devices of the prior art, and it alsosimplifies the replacement of the mercury switch in an outside circuitconnecting unit.

Another object of my invention is to construct a mercury switch whereinthe metallic plunger or mercury displacer will not oxidation.

A still further object of my invention is to provide a seal which willjoin and expand in unison with two elements each of which has adifferent coefiicient of expansion from the other element.

A still further object of my invention is to eliminate or reduce the humwhere the mercury switch of the plunger type is employed in conjunctionwith alternating current.

Other objects of my invention are to provide an improved device of thecharacter described that is easily and economically produced, which issturdy in construction and which is highly efilcient in operation.

With the above and related objects in view, my invention consists in thedetails of construction and combination of parts, as will be more fullyunderstood from the following description, when read in conjunction withthe accompanying drawing, in which:

Fig. 1 is a fragmentary side elevational view of an electric mercuryswitch embodying my invention together with an electromagnet shown inoperative position and a board on which electrical terminals connect thecircuit to the switch.

Fig. 2 is an enlarged perspective view of the ceramic, or insulatingliner adapted to surround the interior surface of the metallic plunger.

Fig. 3 is a perspective view of the magnetizable metal plunger.

Fig. 4 is a plan view of the mercury switch terminal connector and themercury switch attached to the connector.

Fig. 5 is an enlarged sectional view showing a plurality of sealingbeads, each bead having a different coefiicient of expansion.

Fig. 6 shows the magnetic field core which supports the electromagneticcoil E and a cylindrical magnetic ring which interfits with the fieldcore. The magnetic ring assists in lifting the plunger.

Referring now to the drawing, I disclose a hermetically sealed tubularcontainer or envelope, generally designated as A, made of heat resistantglass. The base in of the tube has two spaced electrodes or terminals l2and It pass therethrough so that each electrode extends into the chamberof said glass tube. The electrodes l2, H are preferably composed oftungsten and are surrounded by seals of heat resistant beads l6 and I8,respectively, at the junction of the tubular container and theelectrodes. These beads eventually are fused to the envelope so that anintegral unit is formed.

The electrode I4 is oilset so that it lies within be discolored as bythe vertical center of the tube, and it may be partially encircled orencompassed by a spaced ceramic cylinder or tube, generally designatedas B. The lower end of the ceramic cylinder B may be annealed to andattached to the upper part of a circular heat resistant bead 24, asshall here-' inafter be further explained.

Since the ceramic cylinder and the heat resistant glass have differentcoeificients of expansion, difiiculty has been experienced in unitingthe adjacent ends of such materials because of breakage. I seal twoelements of different coefiicients of expansion together by a series ofbeads or cylinders 20, 22, and 24, each of a different coeflicient ofexpansion in order to allow for the different degrees of expansion. Asan example, the bead or cylinder 20, which has one end joined to the topof the heat resistant bead I 8--the latter encircles the part ofelectrode l4 passing through the envelope Ahas a coeificient ofexpansion almost equal to that of the heat resistant bead. The bead orcylinder 24, having its upper edge joined to the lower end of theceramic cylinder 13, has a coeflicient of expansion almost equal to thatof the mercury retaining cylinder B. The intermediate bead or cylinder22, encircling a part of the electrode l4, has its ends joined to theadjacent ends of the beads 20 and 24 and has a coefiicient of expansionintermediate the coeificient of expansion of the beads 20 and 24. If theabove graded sealings are not sufilcient, additional graduations ofbeads or cylinders having still different coefficients of expansion maybe employed.

Mercury, generally designated as H, fills the lower end of the envelopeA and a part of this mercury fills the hollow ceramic cylinder B whichsurrounds the electrode. The ceramic tube B projects above the electrodel4 which is within the tube, and the mercury therein is in electricalcontact with the electrode.

A hollow cylindrical magnetic plunger or liquid displacer, generallydesignated as P, having an inner quartz or heat resistant glasscylindrical liner 28 is buoyed or floats upon the mercury H within thelower end of the envelope. The metal plunger or armature P is adapted tomove vertically upwardly and downwardly under control of anelectro-magnet, generally designated as E, so that as the'electro-magnetE is energized, the plunger or armature P is pulled downwardly into themercury causing the mercury to rise upwardly over the top of thecylinder L so that the circuit is completed. Upon the electro-magnetbeing deenergized or the flux field being reduced, the plunger will bebuoyed upon the surface of the mercury, and the level of the mercurywill fall because the mercury now displaces the plunger which formerlydisplaced some of the mercury. Hence, a portion of the mercury willremain within the ceramic tube in engagement with the center electrodel4, and the mercury surrounding the outside of the tube will recede to alevel below that of the top of the cylinder. Hence, the circuit will beopened.

It should be particularly noted that the makeand-break of the electricalcircuit is completed solely by a mercury to mercury contact and notagainst either one or the other of the electrodes l2 or l4. In this waythere is no danger of the electrodes being pitted or corroded, and theceramic tube is such that it will not take a coating of mercury; othermaterials, such as glass, may have a coating of metal electro depositedthereon. The use of a ceramic mercury retainer eliminates any permanentcircuit being established within the tube.

The magnetic plunger P is made of a single stamping of magnetizablemetal and has a plurality of small extensions or projections 30 on itsouter curved bounding surface 32; these projections engage the envelopeA, and because they present a small contact surface they reduce frictionbetween the wall of the envelope and the plunger. The plunger has aninwardly extending ridge or a series of inwardly extending indentations34 adjacent its upper edge; the ridge or indentation limits movement ofthe ceramic liner 28 in an upwardly direction as Fig. 1 is viewed. Theplunger P has a plurality of inwardly extending integrally formed tabs36, 38 which engage a portion of the lower end of the ceramic liner 28to prevent the liner from moving in a downwardly direction with respectto the plunger P, as Fig. 1 is viewed. Since the plunger is of a singlestamping, itis formed into a cylindrical shape with its verticallyextending edges 40, 4| spaced apart to form an air gap 42. Since about98% of the mercury switches under discussion are used in alternatingcurrent circuits, the A. C. hum is eliminated or greatly reduced becauseof the air gap. The reason for, the reduction or elimination of the humis that the plunger is unsymmctrically formed with respect to theelecalso aids in the ready sliding of the magnetic plunger when and asit engages the inner wall of the tube. By using an enamel, the cost ofthe plunger is materially reduced and serves as an easy and ready way ofinsulating the shell.

Annealing process Heretofore, the metallic plunger has been decolorizedor oxidized during the annealing process. To prevent the oxidation ordiscoloring of the magnetic alloy of the plunger P in order to eliminatethe expensive bright dipping of the plunger to a saleable condition, theglass unit blank of the envelope is evacuated after the electrodes andmagnetic plunger are placed within the glass envelope, the mercury alonebeing omitted. The lower end of the tube where the electrodes join thetube is then annealed. After the annealing process the tube is opened,mercury is poured therein, then the tube is exhausted so that a vacuumis formed, and the tube is sealed without any decolorization of theplunger.

The switch mounting block In order to facilitate the replacement of themercury switch, I provide a convenient base and terminal connectionillustrated in Fig. 1. The electro-magnet E is formed as a toroid, andthrough its hollow center the switch envelope A is placed so that theplunger P is buoyed on the mercury, and upon the energizing of theelectromagnet E the plunger P-is pulled into the mercury to establish anelectrical contact.

The electrodes l2 and I4 slip into electrical engagement with terminals,generally designated as T and T The terminal T of electrical conductingmetal has a bifurcated end defined by a slot 44 between the parallellegs 46, 41. An enlarged circular-like opening 4. between the legs 46,41 receives one oi the electrodes, and a binding nut ll passing throughan opening 52 in leg 41 and screw-threaded into leg 46 holds theelectrode securely in position. A holding nut 54 passing through athreaded opening 56 at one end of the terminal holds the terminal to thetube and electro-magnet mounting blocks, generally designated as D. Thisfeature eliminates pig-tail leads and also butt-welding of boratedcopper in order to solder the said pig-tail leads to the electrodes.

As the terminals T and T are identically constructed, a description ofone terminal will sumce as a description of both terminals.

The electro-magnet E is held between a magnetic yoke or field structure,generally designated as F. The magnetic yoke or field structure Fcomprises two parallel by a back piece ll. The parallel arms 60 havealigned central openings 64 and 65 therein so that the tube A may passtherethrough, and each of the legs ll, 62 are slotted as at 66, 68,respectively.

A magnetirable ring, generally designated as G, has a slottedcylindrical surface Ill concentric about the inner portion or thetoroidal electromagnetic coil E and is located so that it is between thespaced legs 02. The magnetizable ring G has a flange I2 so that it doesnot slip through the electro-magnetic coil. The slotted magnetic ringassists in lilting the plunger upspaced arms 60, 82 joined wardly in arapid manner. Hence, the time of arcing is diminished.

Although my invention has been described in considerable detail, suchdescription is intended as illustrative rather than limiting, since theinvention may be variously embodied, and the scope of the invention isto be determined as claimed.

I claim as my invention:-

1. A process of treating an electromagnetic actuated mercury switchwherein the magnetic plunger is not discolored comprising the steps offorming an envelope, inserting the magnetic plunger therein, insertingthe electrodes within one end of the tube, compressing said electrodesinto the envelope in a single operation, creating a vacuum within saidenvelope, annealing the tube, inserting mercury within said envelope,exhausing the air therefrom, and sealing the envelope.

2. A process of forming an electromagnetic actuated mercury switch whichcomprises the steps of forming an envelope, stamping a magnetic plunger,forming the plunger so that a small air gap exists between its ends,inserting the magnetic plunger within said envelope, inserting andcompressing the electrodes within said tube, creating a vacuum withinsaid envelope, annealing the tube, inserting mercury within saidenvelope, exhausting the air from said envelope, and sealing theenvelope.

NORMAN MCKINNEY.

